Multi-Rail Parapet

ABSTRACT

A vehicle safety parapet comprises a plurality of rails ( 18, 24, 28 ) supported at varying heights on uprights ( 12 ). A first of the rails comprises a steel box-section supported at each upright by bracketing means ( 20 ) configured to collapse when a horizontal impact load is applied to the rail, such that the first rail is displaced towards the upright. At least one other rail extends from the uprights by a greater distance than the first rail when the bracketing means has collapsed.

The present invention relates to a multi-rail parapet of the type used to prevent a wayward vehicle falling over an edge such as a precipice or the edge of a bridge and to reduce the level of impact severity.

Known parapet designs consist of a series of uprights that support horizontal rails that extend along the roadway side of the uprights. In order to provide protection for different sizes of vehicles, two, three or sometimes more rails are provided at different respective heights above the road level. Parapets are required to meet certain standards set by authorities. In the European Union, the standards, such as EN1317, require crash testing of the parapet. A test vehicle is propelled into a section of the parapet and the effects of the impact are recorded on video and data collection devices. Certain parameters are specified in the standard, which are measured, for example by inspection of the video and test data, to determine whether or not the parapet meets the standard, and to define the parapet designation.

In general, the standards require that the penetration of the vehicle beyond the original parapet line is limited to a certain distance, but at the same time a certain level of safety is provided to the vehicle occupants, which requires that the impact should not cause the parapet, or parts of the vehicle chassis to penetrate the passenger compartment. These criteria place opposing constraints on the parapet design. For a light vehicle such as a small car (standards specify a weight of 900 kg), it is the lowest rail of the parapet, which is subjected to the greatest impact. This must be strong and stiff enough to limit the penetration of the vehicle through the parapet, but if too rigid, the impact loading will be transmitted through the vehicle chassis causing a greater risk to an occupant.

The furthest lateral displacement of the parapet or test vehicle is used to classify the parapet design. For example, a W3 classification is given to a parapet that has a lateral displacement of no more than 1 m. However, it is common for a parapet to be mounted on a relatively narrow plinth, for example many bridge parapet plinths are 450 mm wide. This means that an impacting vehicle will penetrate through a W3 parapet such that the wheels on the impacting side of the vehicle could pass beyond the plinth. When this occurs, the vehicle will start to roll, which in turn causes much greater damage to both the vehicle and the parapet structure. At the same time, the tests are used to provide occupant safety ratings A and B. Limiting the penetration of the vehicle, such that the wheels remain on the plinth would, in general, require stiffening the bottom rail such that a previously acceptable, B-rated parapet could increase to an unacceptable level for many parapet installations.

It is an aim of the present invention to provide a multi-rail parapet design that alleviates the aforementioned problems.

According to the present invention there is provided a vehicle safety parapet comprising a plurality of rails supported at varying heights on uprights, wherein a first of said rails comprises a steel box-section supported at each upright by bracketing means configured to collapse when a horizontal impact load is applied to the rail such that the first rail is displaced towards the upright, and wherein at least one other rail extends from the uprights by a greater distance than the first rail when the bracketing means has collapsed.

When a vehicle strikes the parapet the impact taken by the first rail will initially cause the bracket to collapse towards the upright. Although the first rail is a steel box-section, which has a high inherent stiffness, it behaves like a less stiff rail because of the collapsing bracket. In other words the collapsing bracket acts to cushion the impact. This means that the initial impact is not sufficient for the first rail to cause significant damage to the vehicle at a risk to occupant safety. However, once the first rail makes contact with the upright, the stiffness of the parapet structure is insufficient for the vehicle to penetrate far through the parapet. At this stage, the first rail and collapsing bracket have already reduced the initial impact and momentum of the vehicle without significant damage to the vehicle. Now the stiff first rail limits further movement through the parapet reducing the likelihood of the vehicle's wheels passing beyond the edge.

A further advantage arises because the other rail(s) extend further from the upright when the bracketing supporting the first rail has collapsed under the impact of a vehicle. These other rails will act to restrain any tendency for the vehicle to roll when it impacts the first rail This also means that when a larger vehicle impacts the parapet another, stiffer rail will absorb more of the impact, placing less reliance on the first rail with its collapsible bracket mounting.

In a preferred embodiment, the first rail is a lower rail, the at least one other rail being mounted above the first rail.

In a preferred embodiment, the bracket means comprises at least one sheet metal cleat member having a vertical portion for securing to the upright, a horizontal portion for securing to the first rail, whereby the cleat is operable to collapse by plastic deformation.

The cleat may further comprise an inter-connecting portion adjoining the horizontal and vertical portions at bends such that the plastic deformation occurs at one or more of the bends. In this arrangement, when mounted to the upright, the inter-connecting portion is set at an angle to both the upright and the rail. The length and angle of the interconnecting portion determines the spacing of the rail from the upright.

Preferably the bracket means comprises a pair of cleats mounted to the upright one above the other, a lower cleat supporting the first rail from below, and an upper cleat supporting the first rail from above. More preferably, both cleats have the same dimensions and are mounted in the same orientation. This arrangement provides the advantage that both cleats will deform in the same manner under the impact load resulting in a predictable mode of collapse of the bracketing means.

In a preferred embodiment, the parapet includes a second rail having a trapezoidal section with the shorter parallel side facing the roadway. At least part of the longer parallel side of the second rail, facing away from the roadway, way may be open.

It is an advantage that the trapezoidal cross-section provides a particularly strong and stiff rail section for resisting an impact from a vehicle striking the shorter parallel side. Such a section can be manufactured by folding the section from a sheet of steel in a cold rolling operation. This is significantly less expensive than a steel box section, which is formed by hot-rolling. The open-back section means that it is not necessary to form an enclosed section, as with a box-section rail. The open-back section also allows the rail to be mounted to an upright by means of a simple clamping plate arrangement.

Preferably the second rail is mounted above the first rail and provides a second barrier. It is an advantage that, with a light vehicle, such as a small or medium sized car, the second rail will be impacted by an upper surface of the vehicle. The second rail helps to absorb more of the impact and further limit the penetration of the vehicle. For larger vehicles, the second rail will be impacted before the first rail and will serve to absorb a high proportion of the impact.

In an alternative preferred embodiment, the second rail is another rail having the same, or similar construction and collapsible support bracketing as the first rail. It is an advantage that by providing two rails mounted one above the other on collapsible brackets, the cushioning effect of an impact will occur for both small and medium sized vehicles.

The steel box-section of the first and/or the second rail may be a square section. Alternatively, the steel box section may be rectangular. Preferably, the rectangular box section is orientated with the longer side of the rectangle horizontal.

Preferably, a third rail is provided mounted above the first and second rails. It is an advantage that the third rail restrains rolling of small and medium sized vehicles impacting the parapet, and also provides a barrier for larger vehicles.

An embodiment of the invention will be described with reference to the following drawings.

FIG. 1 is a cross-section through a 3-rail parapet and an upright.

FIG. 2 is a detailed cross-section through a first rail of the parapet of FIG. 1.

FIG. 3 is a detailed cross-section through a second rail of the parapet of FIG. 1.

FIG. 4 is a cross-section through another 3-rail parapet and an upright.

Referring to FIG. 1, a parapet 10 consists of a series of uprights 12, one of which is shown. The uprights 12 are mounted to a plinth 14 that defines an edge of a roadway next to a drop. The edge may be an edge of a bridge or a precipice. The plinth 14 is constructed of concrete with a width of 450 mm, as commonly used on bridges. An anchoring arrangement 16 is used to secure each upright 12 through a baseplate 15 to the plinth 14. The uprights 12 support three rails 18, 24, 28, which run past the uprights on the roadway side.

A first rail 18 has a square steel box section supported from each upright 12 by a bracket arrangement having a lower cleat 20 and an upper cleat 22. This will be described in more detail below with reference to FIG. 2. A second rail 24 has a trapezoidal cross-section and is mounted to each upright by means of a clamping plate 26. This will be described in more detail below with reference to FIG. 3. A third rail 28 has a square steel box section supported from each upright 12 by another bracket arrangement having a lower cleat 30 and an upper cleat 32.

Referring to FIG. 2, the first rail 18, which forms the lowest of the three rails, is supported from below by the lower cleat 20, and from above by the upper cleat 22. The upper cleat 22 has the same shape and dimensions as the lower cleat 20, and is mounted to the upright 12 in the same orientation as the lower cleat 20. The lower cleat 20 is formed of a length of steel strip having two bends 21 a, 21 b, which define a vertical portion 20 a, a horizontal portion 20 b and an inter-connecting portion 20 c. The vertical portion is secured to the upright 12 by means of a lower screw fixing 34. Similarly the vertical portion of the upper cleat 22 is secured to the upright 12 by means of an upper screw fixing 36. The first rail 18 is sandwiched between the horizontal portion 20 b of the lower cleat 20 and the equivalent horizontal portion of the upper cleat 22. A vertical bolt 38 passes through the first rail 18 and both cleats and is secured by a nut 40.

The lower cleat 20 and the upper cleat 22 are fabricated from steel strip having a thickness selected such that when a vehicle strikes the first rail 18 and applies a certain minimum horizontal impact load, both cleats will collapse due to plastic deformation at the bends 21 a, 21 b. The impact load at which the cleats collapse is determined by design of the cleats. Although the first rail is a steel box-section, which has a high stiffness, it behaves like a less stiff rail because of the collapsing bracket. This means that the initial impact is not sufficient for the first rail to cause significant damage to the vehicle at a risk to occupant safety.

The collapsible bracket arrangement of the lower cleat 20 and the upper cleat 22 are provided on the first rail 18 because it is this rail, which will be struck by the wheels or lower parts of a smaller vehicle. It is on smaller vehicles where the occupants are seated closer to the vehicle chassis, where there is a greater risk of injury to an occupant when the vehicle strikes a low parapet rail. This is because the impact of the rail is transmitted directly into the chassis, which may buckle or break such that part of the chassis may penetrate into the occupant's compartment.

When the cleats 20, 22 collapse far enough for the first rail 18 to come into contact with the upright 12, a much stiffer barrier is presented to the vehicle. The first rail and collapsing bracket have already reduced the initial impact and momentum of the vehicle without significant damage to the vehicle. At this point the parapet is designed to absorb more of the impact such that the upright 12 begins to yield and transfer load via the baseplate 15 to the anchorage 16. The stiffer barrier will result in less deflection of the parapet structure for a given impact, such that the wheels of a vehicle impacting the parapet side-on will not pass beyond the plinth 14. If the wheels were to pass beyond the plinth, the vehicle would tend to roll and when this occurs there is a much greater risk of damage to the vehicle as well as to the parapet structure. If an impacting vehicle deflects a parapet structure beyond the edge of a bridge, and the structure itself is damaged, there is a much greater risk of materials falling off the bridge and causing a hazard to whatever may be below. With the present invention the stiffer parapet structure reduces the possibility of this hazard, while retaining a degree of occupant safety in the impacting vehicle.

Referring to FIG. 3, the second rail 24 has a trapezoidal cross-section with a shorter parallel side 24 a facing the roadway and secured to the uprights at positions on the opposite, longer parallel side. The trapezoidal section of the second rail 24 is not a closed section, but has an open back between short flange portions 24 b, 24 c. To secure the second rail 24 to an upright 12, the clamping plate 26 overlaps the flange portions 24 b, 24 c so as to trap them between the clamping plate 26 and the upright 12. The clamping plate is secured to the upright by means of screw fasteners 42.

The trapezoidal cross-section of the second rail 24 is somewhat larger than the cross section of the square box-section of the first rail 18. It has been found that this cross-section provides a strength and stiffness of rail that is comparable to that of a square box-section, but can be fabricated from sheet steel using a cold-rolling process, making a much less expensive, but equally effective rail. However, unlike the hot-rolled square section rails (such as the first rail 24 and the third rail 28), the trapezoidal second rail will absorb more of the impact of a vehicle by deformation of the rail cross-section. A vehicle impacting on the parapet 10 of FIG. 1 will, in general, strike the second rail 24 first, and this rail will start to collapse, absorbing some of the impact load and “softening” the impact. The trapezoidal shape of the cross-section ensures that the cross-section does not collapse completely under the impact, a greater portion of the impacting load being transmitted to the upright 12 than would be the case if, for example, and equivalent size of square or rectangular section was used.

Referring again to FIG. 1, the third rail 28 is mounted to the upright 12 by means of a lower cleat 30, of the same type as used on the first rail 18, and a top cleat 32. The top cleat 32 has a single right-angle bend. This cleat is stronger than the lower cleat 30 and will not collapse in the same way. The third rail 28 is much higher above the roadway than the first and second rails, and its main function is to act as a barrier for larger vehicles. In this case it is appropriate to use a stiffer rail construction than for the first and second rails, the principal objective being to limit the penetration of the vehicle past the original line of the parapet. However, it is convenient to use the same cleats wherever possible, which is why the lower cleat 30 is of the same type as used for mounting the first rail 18.

Referring to FIG. 4, in an alternative arrangement a parapet 100 consists of uprights 112 mounted through a baseplate 115 to a plinth 114 by anchoring means 116, in the same manner as described above for the parapet 10 of FIG. 1. The uprights 112 support three rails 118, 124, 128 on the roadway side. First and second rails 118, 124 are of substantially the same rectangular steel box section supported from each upright 112 by collapsible bracket arrangements having, respectively, a lower cleat 120, 125 and an upper cleat 122, 126. As in the parapet 10 of FIG. 1, the third rail 128 has a square steel box section.

The parapet 100 is designed to provide a cushioned impact to both small and medium sized vehicles by way of the first and second rails 118, 124. It has been found that, by providing two lower rails supported by collapsible brackets, the parapet can more effectively withstand the impacts of a wider range of vehicle sizes. Thus most of the impact of a small vehicle will be imparted through the first, lower rail 118, in the same manner as described above for the parapet 10 of FIG. 1. However, for a medium sized vehicle the second rail 124 will absorb more of the impact. The third rail 128 helps to restrain rolling of impacting vehicles and acts as a barrier to absorb an impact from a larger vehicle.

The first and second rails 118, 124 are of rectangular cross-section, mounted with the longer side of the rectangle horizontal. This provides a stiffer rail than the square rail 18 of the parapet 10 of FIG. 1. Although the first and second rails 118, 124 are intended to cushion the initial impact of a vehicle, the collapsible brackets provide the cushioning effect. A stiffer rail ensures that the rail itself does not bend under the initial impact, but transmits the impact to the collapsible brackets. Once the brackets have fully collapsed, it is desirable for the rails to be relatively stiff to prevent the parapet from being deflected too far and to keep the vehicle on the bridge. 

1-16. (canceled)
 17. A vehicle safety parapet comprising a plurality of rails supported at varying heights on uprights, including: a first rail comprising a steel box-section supported at each upright by bracketing means configured to collapse when a horizontal load from a vehicle impacting the parapet is applied to the rail such that the first rail is displaced towards the uprights; and a second rail mounted at a height at which an impacting vehicle of a first size would be expected to impact the second rail after the first rail has been displaced towards said uprights, wherein the first and second rails extend substantially the same distance from the uprights.
 18. The vehicle safety parapet of claim 1, wherein the first rail is a lower rail, the second rail being mounted above the first rail.
 19. The vehicle safety parapet of claim 1 wherein the second rail comprises a steel box-section supported at each upright by bracketing means configured to collapse when a horizontal load from a vehicle impacting the parapet is applied to the rail such that the second rail is displaced towards the uprights; and the second rail mounted at a height at which an impacting vehicle of a second size would be expected to impact the second rail first.
 20. The vehicle safety parapet of claim 1, wherein the second rail has a trapezoidal section with the shorter parallel side facing the roadway.
 21. The vehicle safety parapet of claim 4, wherein at least part of the longer parallel side of the second rail, facing away from the roadway, is open.
 22. The vehicle safety parapet of claim 1, wherein the bracket means comprises at least one sheet metal cleat member operable to collapse by plastic deformation.
 23. The vehicle safety parapet of claim 6, wherein the cleat member has a vertical portion for securing to the upright and a horizontal portion for securing to the first rail.
 24. The vehicle safety parapet of claim 7, wherein the cleat further comprises an inter-connecting portion adjoining the horizontal and vertical portions at bends such that the plastic deformation occurs at one or more of the bends.
 25. The vehicle safety parapet of claim 8, wherein, when mounted to the upright, the inter-connecting portion is set at an angle to both the upright and the rail.
 26. The vehicle safety parapet of claim 6, wherein the bracket means comprises a pair of cleats mounted to the upright one above the other, a lower cleat supporting the rail from below, and an upper cleat supporting the rail from above.
 27. The vehicle safety parapet of claim 10, wherein both cleats have the same dimensions and are mounted in the same orientation.
 28. The vehicle safety parapet of claim 3, wherein the second rail is another rail having the same, or similar construction and collapsible support bracketing as the first rail.
 29. The vehicle safety parapet of claim 12, wherein the steel box-section of the first and/or the second rail is a square section.
 30. The vehicle safety parapet of claim 12, wherein the steel box section is rectangular.
 31. The vehicle safety parapet of claim 14, wherein the rectangular box section is orientated with the longer side of the rectangle horizontal.
 32. The vehicle safety parapet of claim 1, wherein a third rail is provided mounted above the first and second rails.
 33. A vehicle safety parapet comprising a plurality of rails supported on uprights, each rail being supported at a different height, the safety parapet including: first and second rails, each comprising a steel box-section supported at each upright by bracketing means configured to collapse when a horizontal load from a vehicle impacting the parapet is applied to the rail such that the rail is displaced towards the uprights, wherein the second rail is mounted at a height at which an impacting vehicle of a first size would be expected to impact the second rail after the first rail has been displaced towards said uprights, and at which an impacting vehicle of a second size would be expected to impact the second rail first, wherein the first and second rails extend substantially the same distance from the uprights.
 34. A vehicle safety parapet comprising a plurality of rails supported at varying heights on uprights, including: a first rail comprising a steel box-section supported at each upright by bracketing means configured to collapse when a horizontal load from a vehicle impacting the parapet is applied to the rail such that the first rail is displaced towards the uprights; and a second rail mounted at a height at which an impacting vehicle of a first size would be expected to impact the second rail after the first rail has been displaced towards said uprights, wherein the bracket means comprises at least one sheet metal cleat member having a vertical portion for securing to the upright, a horizontal portion for securing to the rail and an inter-connecting portion adjoining the horizontal and vertical portions at bends such that the bracket means collapses by plastic deformation occurring at one or more of the bends. 